1. Field of the Invention
This invention pertains to friction wheel distance measuring devices and instruments. More specifically, it pertains to such devices which are essentially mechanical and which include an internal mechanism, coupled between the friction wheel and a visual measurement readant, which is switchable to cause the readout to represent measurements in either the English measurement system or the metric measurement system.
2. Review of the Prior Art
Friction wheel distance measuring devices are well known and have gained wide use as accessories for machine tools and the like. The precision, accuracy, reliability and effectiveness of such devices are so great and so well recognized that such devices have themselves then adopted as principal components of precision testing and measuring machines, such as height gages and machine tool control systems. The most widely known friction wheel measuring device is marketed worldwide under the trademark "TRAV-A-DIAL", and is a principal component of measuring systems sold under the trademarks "TEDD" and "TRAK" and of machine tool control systems sold under the trademark "TEDD Command".
(Strictly speaking, products currently manufactured under the trademarks mentioned above do not rely upon friction between the wheels thereof and the surfaces along which the wheels roll in use. Current products bearing or sold under these marks incorporate the improvement described in U.S. Pat. No. 3,771,228, and thus rely on a self-generated microscopic rack and pinion effect in the interface between the wheel and the surface along which it rolls in use. Products of this type have come to be known, however, as "friction wheel measuring devices", and it is in this art-recognized sense that this term is used in the present document.)
TRAV-A-DIAL measuring devices are manufactured by the assignee of the present invention; such devices, and also the measuring and machine tool control systems of which such devices of their principal mechanisms are components, are sold in the United States and elsewhere by Southwestern Industries, Inc., Los Angeles, California.
U.S. Pat. Nos. 3,307,265, 3,311,985, 3,561,121, and 3,771,228, for example, all owned by the assignee of this invention, pertain to TRAV-A-DIAL measuring devices.
Friction wheel measuring devices in their purest form, and as first introduced, are entirely mechanical devices in which a hardened steel metering wheel of known circumference is coupled by a motion amplifying gear train to a visual readout mechanism. In use, the housing of the device, from which the rim of the metering wheel protrudes, is mounted to one of two relatively movable parts, such as a lathe carriage, for forceful rolling contact of the wheel rim with the other of the two movable parts, such as a lathe bed. As the lathe carriage is moved along the lathe bed, for example, the wheel rolls faithfully without slippage along the lathe bed. The amount of rotation of the wheel is thus directly related to the distance the carriage is moved along the lathe bed. Since the circumference of the wheel is known, the indication of wheel rotation presented by the readout mechanism is an accurate measurement of the distance movement of the lathe carriage along the lathe bed.
The first TRAV-A-DIAL measuring devices were structured to cause measurements made to be displayed in the English measurement system, i.e., in inches and in tenths, hundredths and thousandths of an inch. Later, a different arrangement of this device was produced which caused measurements made to be displayed in the metric measurement system, i.e., in millimeters and in tenths and hundredths thereof. These devices were entirely mechanical, and different devices were needed to obtain measurements in the different measurement systems. See U.S. Pat. Nos. 3,311,985 and 3,378,929.
Thereafter, an electronically operated remote readout mechanism was developed for use with TRAV-A-DIAL measuring devices. To enable the remote readout to be used, a signal generator was incorporated into the measuring device, the generator output signals being supplied to and operated on by the remote readout which displayed the measurement made by the wheel in the same units of measure as shown by the original readout mechansim which was retained in the measuring device itself; see British Pat. No. 1,189,323.
The advantages of the remote readout were, among others, that it could display measurements of distances greater than a single revolution of the metering wheel, and could be located in a place more easily seen by the user than the measuring device itself which, by necessity due to the nature of the machine tool, might have been mounted in an obscured location. Also, by appropriate manipulation in the remote readout of the signals supplied to it in response to operation of a mode selector later made a part of the remote readout, it was possible to cause the remote readout to display measurements of interest in units of either the English or the metric measurement systems. These remote readout measurement systems were and are substantially more expensive than the purely mechanical measuring devices, and were and are marketed under the trademark TEDD.
A variation of the TEDD distance measurement system is the TRAK measurement system in which the friction wheel, gear train and signal generator assembly, mounted to the machine tool, has no visual readout mechanism itself and functions as a displacement sensor and signal generator for a digitally displaying remote readout. TRAK measurement systems also display measurements of interest in either English or metric units of measure. These systems are also more costly than the purely mechanical TRAV-A-DIAL measuring devices.
For many years, industry has produced machined parts dimensioned in either English or metric units of measure. In Europe, products made for export to the United States or to England, for example, were made with parts dimensioned in English units of measure, whereas the same products intended for European or other sale incorporated parts dimensioned in metric units of measure. More recently, United States industry has increasingly produced parts dimensioned metrically; this has been done to make United States products more salable abroad. Also, it may have been done in anticipation of the conversion from English to metric measurement systems which is now well underway in England and is beginning in the United States. Today, it is common for United States designers of machined parts to dimension the parts either both in English and metric units, or only in metric units.
It has been determined that a need, and therefore also a market, exists for purely mechanical distance measuring devices which are of relatively low cost and which can display measurements of interest in either English or metric units of measure. Heretofore, as shown above, separate devices were required to provide English and metric units of measure, unless one was willing to use the more costly measuring systems having remote readout and display units.
This need is reflected by the availability of machine tool conversion dial assemblies which, when installed in a machine tool such as a lathe, enable measurements to be made in either English or metric units. One such conversion dial assembly is manufactured by Sipco Machine Co., Marion, Massachusetts, and has separate English and metric scales both of which are visible to the tool operator. Another conversion dial has a single scale which, by movement of datum lines, is readable either in English or metric units; this dial assembly is manufactured by Jergens Inc., Cleveland, Ohio; see U.S. Pat. No. 3,651,780. Both the Sipco and Jergens dials connect to the tool leadscrew and are susceptible to all errors in the leadscrew. Both use a planetary gear drive; in the Sipco dial both scales are driven, and in the Jergens dial the planetary is locked when the mechanism is in its "English" operating mode. Neither arrangement is sufficiently compact to enable use in a friction wheel measuring device. Also, these dial assemblies are themselves expensive. The need identified above still has not been fully satisfied by the prior art.